[lworld] RFR: 8281166: [lworld] javac should generate BSM to invoke the static factory for value class

[Srikanth Adayapalam]

On Mon, 7 Feb 2022 07:57:43 GMT, Rémi Forax <forax at openjdk.org> wrote:

> I wonder if the transformation from a constructor call to a static method call when it's a value class should not be done before the lambda transformation ?

This is technically feasible, but has some practical complications. As the top level comment in com.sun.tools.javac.jvm.TransValues calls out:


/**
 * This pass translates value class constructors into static factory methods and patches up constructor
 * calls to become invocations of those static factory methods.
 *
 * We get commissioned as a subpass of Gen. Constructor trees undergo plenty of change in Lower
 * (enclosing instance injection, captured locals ...) and in Gen (instance field initialization,
 * see normalizeDefs) and so it is most effective to wait until things reach a quiescent state
 * before undertaking the tinkering that we do.
 *
 * See https://bugs.openjdk.java.net/browse/JDK-8198749 for the kind of transformations we do.
 *
 */


Lambda lowering happens well before Lower and Gen pipeline phases. TransValues is a subphase of Gen - we need to wait until Gen because constructors undergo lots of changes up until and well into Gen. So if we want to group all transformations - of constructors into static factories and constructor invocations into static value factory invocations - into one centralized localized pipeline stage (i.e TransValues) the present approach is the best

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PR: https://git.openjdk.java.net/valhalla/pull/629